Thin-Film Coating with Reduced Optical Reflectivity Based on a Nanoporous Germanium Layer

Electromagnetic (EM) wave emissions from wearable or flexible smart display devices can cause product malfunction and have a detrimental effect on human health. Therefore, EM shielding strategies are becoming increasingly necessary. Consequently, herein, we prepared a transparent acrylic polymer-coated/reduced graphene oxide/silver nanowire (Ag NW) (A/RGO/SANW) EM interference (EMI) shielding film via liquid-to-vapor pressure-assisted wet sintering. The film exhibited enhanced Ag NW network formation and antireflection (AR) effects. The wet-sintered Ag NW shielding film had a threshold radius of curvature (ROC) of 0.31 mm at a film thickness of 100 μm, demonstrating its high flexibility, whereas the conventional indium tin oxide (ITO) shielding film had a threshold ROC of ∼5 mm. The EMI shielding effectiveness (SE) of the A/RGO/SANW multilayer film was approximately twice that of the ITO film at a similar relative transmittance (84-85%). The optical relative reflectance of the Ag NW layer was reduced due to the AR effect, and the visible-light transmittance was considerably improved owing to the different refractive indices in the multilayer shielding film. Because the acrylic coating layer had a high contact angle, the multilayer film exhibited high temperature and humidity durability with little change in the SE over 500 h at 85 °C and 85% relative humidity. The multilayer film comprising wet-sintered Ag NW exhibited high flexibility and humidity durability, high shielding performance (more than 24 dB at a relative transmittance of 85% or more), and high mass productivity, making it highly applicable for use as a transparent shielding material for future flexible devices.

Synthesis of multiple layers of alternating ZnO and TiO2 using atomic layer deposition and their optical characterization

In recent years, ultrashort pulsed laser micromachining of multi-layer metal film assembly had attracted great attention because the multi-layer configuration can be well applied for satisfaction of thermal, optical and electronic requirements in development of MEMs, photoelectric equipments and biochips (Liu, 2007). Generally, the thermal properties for metals are physically originated from the collision mechanisms for electron-electron and electron-phonon in the metal targets. For the multi-layer metal film assembly, the thermal properties, such as the electron-phonon coupling strength can actually vary significantly for different layers of the assembly, so the heating of muti-layer film assembly would take on various characteristics for different padding layer configurations. In this article, the ultrafast heating characteristics in multi-layer metal film assemblies irradiated by femtosecond laser pulse were investigated by numerical simulations. The effect of different padding layer configurations on the ultrafast thermalization characteristics for the multi-layer metal film assemblies are well discussed. The ultrafast heat transfer processes in the layered metal film systems after the femtosecond pulse excitation are described based on the two temperature model (TTM), in which the electron and phonon is considered at two different temperatures, and heat transfer is mainly due to the hot electron diffusion among the sub-electron system and the electron energy transfer to the local lattice characterized by the electron-phonon coupling strength. The thermal properties for the respective metal film layers and the optical surface reflectivity are all defined as temperature dependent parameters in order to well explore the ultrafast heating characrastics of the multi-layer metal assemblies. The coupling two temperature equations are calculated by the Finite Element Method (FEM) with respect to temperature dependent thermal and optical properties. The ultrafast two-dimension (2-D) temperature field evolutions for electron and phonon subsystems in the multi-layer metal film assemblies are obtained, which show that the electron and phonon temperature field distributions can be largely effected by adjusting padding layer configurations. The physical origins for the discrepant temperature field distributions in multi-layer film assemblies are analyzed in details. It indicates that electron-phonon coupling strength and phonon thermal capacity play key roles in determining the temperature field distributions of the multi-layer film assembly.

Anodic oxidation of Al/Ge/Al multilayer films

In this article, the optical properties of the multilayer films of SiO2/W/SiO2 for solar selective absorber fabricated by sputtering deposition are simulated and fabricated. The optical properties of the multilayer films with the various layer thicknesses are studied. And the relationships between the film thickness and the optical reflectance are found. An area of the contour map of the optimized photo-thermal conversion efficiency (PTCE) more than 92% for solar selective absorber layer is found. One SiO2/W/SiO2 multilayer film with the thickness of 96/7/87 nm that has the maximum PTCE of more than 94% is simulated and fabricated.

Effect of the thickness of the individual layers in Al2O3/Pt/Al2O3 solar absorber films on the photo-thermal conversion efficiency for rapid industrial production

Electrooptical and structural studies on self-assembled films composed of CdSe nanoparticles, poly(p-phenylene vinylene) (PPV), and different nonconjugated polyelectrolytes are reported. It is demonstrated by optical spectroscopy and X-ray reflectivity measurements that CdSe nanoparticles and PPV can successfully be incorporated into homogeneous ultrathin films by the self-assembly method. The surface roughness obtained from the X-ray measurements is 2.7 and 1.3 nm respectively for CdSe/PAH (PAH, poly(allylamine) hydrochloride) and PSS/PPV (PSS, poly(styrenesulfonic acid)) multilayer films. This allows us to stack a (PSS/PPV)*n film on top of a (CdSe/PAH)*n film to build up well-defined two-layer composite film devices. Electroluminescence studies show that pure (PSS/PPV)*n film devices exhibit green light emission but with a very short lifetime (several seconds) if operated in ambient air. During operation, the PPV emission shifts toward the blue, which indicates that the mean conjugation length of PPV i...

Fifty years ago, who could have imagined that silicon dioxide—the material of ordinary beach sand—would become one of the most important materials of present-day optics and electronics? Yet SiO2is arguably the most crucial material component in current-generation fiber optics and metal-oxide-semiconductor (MOS) device technology. In MOS field-effect transistors (MOSFETs), SiO2serves not only as the gate insulator, but also as the “field oxide” (which isolates various components of an integrated circuit) and as the packaging material which seals the device from outside contamination. In these roles silica acts as a “perfect dielectric,” being characterized by an essentially infinite resistivity (actually ~1016Ohm · m at 300 K). The ability to form such a high quality dielectric film with a near-perfect lattice match on single-crystal silicon continues to favor silicon-based MOS technology over technologies founded on electrically superior GaAs.In the rapidly developing fiber optic arena, fused silica is still “king” due to a combination of properties, including extremely high transparency over a range of usable wavelengths (Figure 1), low material dispersion (~0 at 1.3/üm), high tensile strength (~ 150 kpsi), and high chemical durability. In addition, bulk forms of silica continue to find application in lenses, prisms, windows, and low-coefficient-of-thermal-expansion reflective optics; thin silica films are common components of the highly reflective and anti-reflective surface coatings which are laid down on reflective and transmissive optics, respectively.

Laser damage resistance is a key factor for the improvement of high power laser system. The PETAL laser, developed by the CEA-CESTA (France), uses meter scale reflective optics to compress, transport and focalize sub-picosecond laser pulses at 1053nm with high-energy [1]. In the case of defect-free material, laser-induced damage in the sub-picosecond regime is known to be deterministic since the threshold depends only on the electronic structure of the irradiated materials, the pulse duration and the enhancement of the electric fields in thin film coatings. Based on this consideration, a mono-shot technique has been investigated to assess the intrinsic damage resistance of optical component with only one laser shot. On the other hand, while considering real optical components, manufacturing processes included nanoscale defects in the functional coating. These defects can be ejected when irradiated and strongly reduce the laser damage resistance of optics: rasterscan procedure has then been developed to determine defect-induced damage densities. These densities are found to be high even for fluences well below the intrinsic Laser-Induced Damage Threshold and they increase with the fluence. These experiments bring new information on the operating characteristics of optics in short pulse regime. Once damage is triggered, its evolution under subsequent irradiations has also been studied. Growth experiments have been compared to numerical simulations. The investigations on growth behavior allow a better estimation of the functional lifetime of an optic in its operating conditions. The whole of results, damage initiation and damage growth, is discussed to the light of the laser damage observed on PETAL optics.

Laser damage resistance is a key factor for the improvement of high power laser system. The PETAL laser, developed by the CEA-CESTA (France), uses meter scale reflective optics to compress, transport and focalize sub-picosecond laser pulses at 1053nm with high-energy [1]. In the case of defect-free material, laser-induced damage in the sub-picosecond regime is known to be deterministic since the threshold depends only on the electronic structure of the irradiated materials, the pulse duration and the enhancement of the electric fields in thin film coatings. Based on this consideration, a mono-shot technique has been investigated to assess the intrinsic damage resistance of optical component with only one laser shot. On the other hand, while considering real optical components, manufacturing processes included nanoscale defects in the functional coating. These defects can be ejected when irradiated and strongly reduce the laser damage resistance of optics: rasterscan procedure has then been developed to determine defect-induced damage densities. These densities are found to be high even for fluences well below the intrinsic Laser-Induced Damage Threshold and they increase with the fluence. These experiments bring new information on the operating characteristics of optics in short pulse regime. Once damage is triggered, its evolution under subsequent irradiations has also been studied. Growth experiments have been compared to numerical simulations. The investigations on growth behavior allow a better estimation of the functional lifetime of an optic in its operating conditions. The whole of results, damage initiation and damage growth, is discussed to the light of the laser damage observed on PETAL optics.

A new generation of surface plasmonic optical fibre sensors is fabricated using multiple coatings deposited on a lapped section of a single mode fibre. Post-deposition UV laser irradiation using a phase mask produces a nano-scaled surface relief grating structure, resembling nano-wires. The overall length of the individual corrugations is approximately 14 &mu;m with an average full width half maximum of 100 nm. Evidence is presented to show that these surface structures result from material compaction created by the silicon dioxide and germanium layers in the multi-layered coating and the surface topology is capable of supporting localised surface plasmons. The coating compaction induces a strain gradient into the D-shaped optical fibre that generates an asymmetric periodic refractive index profile which enhances the coupling of the light from the core of the fibre to plasmons on the surface of the coating. Experimental data are presented that show changes in spectral characteristics after UV processing and that the performance of the sensors increases from that of their pre-UV irradiation state. The enhanced performance is illustrated with regards to change in external refractive index and demonstrates high spectral sensitivities in gaseous and aqueous index regimes ranging up to 4000 nm/RIU for wavelength and 800 dB/RIU for intensity. The devices generate surface plasmons over a very large wavelength range, (visible to 2 <i>&mu;</i>m) depending on the polarization state of the illuminating light.

Flexible plasmon metasensor devices describe the use of multiple Ag/Al2O3/mica layers for tunable plasmonic resonances and are a promising research direction. Here, we report on a flexible Ag/Al2O3/mica multilayer platform and its excellent performance on flexible biosensors and photon-emitting devices. In our approach, muscovite (mica) was adopted as a single-crystal substrate due to its optical transparency and mechanical flexibility. The Ag/Al2O3/mica multilayer film is characterized by X-ray diffraction and transmission electron microscopy. Optical, plasmonic, and biosensing studies of Ag/Al2O3/mica multilayers are performed for detailed understanding. A combination of optical absorption, numerical simulations, and optical reflectance measurements has confirmed the biosensor performance. Two kinds of flexible plasmonic device applications are reported here, including (1) plasmonic biosensors with high refractive index sensitivities and (2) significantly enhanced spontaneous photoluminescence (PL) of monolayer tungsten disulfide (WS2) spectra. We found that the PL emission under 0.4 mm-1 curvature bending state increased to 16% compared to the unbent state and redshift of 60 meV/% strain in the emission of WS2 monolayer. Furthermore, the Ag/Al2O3/mica multilayer film displays robust stability and strong endurance up to a bending curvature of 0.4 mm-1. This study shows great potential to be used for biosensors and flexible optoelectronics.

The problem of the photothermal modulation of optical beams passing through multilayer films is an extremely complex one owing to the inhomogeneously modulated refractive index combined with multiple optical reflections inside the sample. This problem has so far not been given an exact analytical treatment in the field of photothermal probing. We consider here such a treatment for normal-incidence optical probing in reflectance of photothermally modulated single-layer thin-film samples with arbitrary optical constants. The validity of the method is demonstrated by application to a thin transparent film of silica on a silicon substrate.

Multilayer optical reflection filters with several kinds of graded refractive index profiles were designed. The effects of the number of layers of multilayer films and grading functions of refractive index profiles on the optical filter characteristics were examined by using simulation. A 33-layer optical reflection filter with a linear refractive index profile was found to be optimal in terms of both optical performance and manufacture. The designed 33-layer TiO2–SiO2 reflection filter was fabricated by helicon plasma sputtering. The optical performance of the prepared multilayer film agreed well with that of the designed filter. The measured transmittance spectrum exhibited a sharp cutoff stop band around a central wavelength of 1340 nm and a wide pass region with high transmittance of about 90%. The reflectance of the stop band was greater than 99.0% in the wavelength region from 1208 to 1518 nm.

Forced assembly polymer coextrusion utilizes layer multiplication to produce films with tens or thousands of micrometer to nanometer thick layers. The development of novel uneven split layer multiplying dies has produced gradient multilayer films with at least a 10 times difference between the thickest and thinnest layers. Coextrusion through a series of equal and uneven split multiplier dies allows for flexibility in the unique design of layer thickness distributions by: (1) altering the multiplier offset and (2) changing the sequence of a series of uneven split multiplying dies with different splitting ratios. This new technology has created highly reflective, multilayered photonic films with gradient layer thickness distributions exhibiting, as examples, a 600 nm wide reflection band and dual optical reflection bands within a single film. Also, gradient multilayers exhibit unique mechanical behavior. A layer thickness dependent craze to shear banding deformation mechanism was observed. In addition, gradient controlled buckling was observed across a single film due to foaming-induced layer delamination.